1. Field of the Invention
The present invention relates to a solid state detector in which a substrate and a photo-conductive layer for generating charges upon irradiation of recording electromagnetic waves, which hold image information, are integrally laminated. The present invention relates also to a solid state detector in which a substrate and a photo-conversion layer for emitting light upon the irradiation of the recording electromagnetic waves are integrally laminated.
2. Description of the Related Art
In radiography performed for the purpose of medical diagnoses and the like, a radiation image recording/reading apparatus which uses a radiation solid state detector to detect radiation and output image signals expressing radiation image information, has been known. As the radiation solid state detector used in this apparatus, various types of detectors have been proposed and put into practical use.
In terms of charge generation processes for converting radiation into charges, there is, for example, a photo-conversion type radiation solid state detector which obtains signal charges by detecting fluorescence, which is emitted from a fluorescent substance upon irradiation of the radiation, by a photoelectric transducer thereof, where signal charges are to be stored in a charge storage portion of the photoelectric transducer, after which the storage charges are converted to an image signal and outputted (for example, U.S. Pat. No. 4,803,359 and Japanese Unexamined Patent Publication No. 2(1990)-164067, PCT International Publication No. WO92/06501, and SPIE Vol. 1443 Medical Imaging V; Image Physics (1991), pp. 108–119 etc.). There is also a direct conversion type radiation solid state detector which collects signal charges generated in a photo (radiation)-conductive layer upon irradiation of radiation by a charge collection electrode thereof, to be temporarily stored in a charge storage portion, where the storage charges are converted to an electrical signal and outputted (MATERIAL PARAMETERS IN THICK HYDROGENATED AMORPHOUS SILICON RADIATION DETECTORS, Lawrence Berkeley L. University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto, Calif. 94304, Metal/Amorphous Silicon Multilayer Radiation Detectors, IEEE TRANSACTIONS ON NUCLEAR SCIENCE. VOL. 36. NO. 2. APRIL 1989, and Japanese Unexamined Patent Publication No. 1(1989)-216290 etc.).
Furthermore, in terms of charge reading-out processes for reading out stored charges to the outside, there is a TFT (thin film transistor) readout type solid state detector for scanning-driving TFTs coupled to a charge storage portion to read out the stored charges. There is also an optical readout solid state detector for irradiating reading light (reading electromagnetic wave) thereto to read out the charges.
In addition, there has been proposed an improved direct conversion type radiation solid state detector in U.S. Pat. Nos. 6,268,614 and 6,376,857. The improved direct conversion type radiation solid state detector adopts a direct conversion type and an optical readout type. The improved direct conversion type radiation solid state detector is constituted by sequentially laminating a first electrode layer which is transmissible by recording radiation; a photo-conductive layer for recording, which exhibits photo-conductivity (to be precise, radiation conductivity) upon irradiation of recording radiation, which transmits through the first electrode layer; a charge transport layer acting substantially as an insulative substance for charges of the same polarity as that of charges held in the first electrode layer and acting substantially as a conductive substance for charges of the opposite polarity to that of the charges; a photo-conductive layer for reading, which shows photo-conductivity (to be precise, electromagnetic wave conductivity) upon irradiation of a reading electromagnetic wave; and a second electrode layer which is transmissible by the reading electromagnetic wave. The improved direct conversion type radiation solid state detector stores signal charges (latent image charges), which hold image information, in an interface (storage portion) between the photo-conductive layer for recording and the charge transport layer.
Herein, in the above described direct conversion type and improved direct conversion type radiation solid state detectors, the photo-conductive layer is usually formed on a substrate made of glass or the like. Furthermore, also in the photo-conversion type radiation solid state detector, a photo-conversion layer containing a fluorescent substance and the like, which converts radiation to light, is formed on a substrate made of glass or the like.
However, when the photo-conductive layer or the photo-conversion layer is laminated to the substrate made of glass or the like as described above, a thermal expansion coefficient of the photo-conductive layer or the photo-conversion layer differs from that of the substrate. This leads to deformation of the photo-conductive layer or the photo-conversion layer as a result of temperature change in the environments thereof. Extreme deformation leads to the deformation of a read out radiation image, and the possibility of a breakdown of the radiation solid state detector.